1. Field of the Invention
The present invention relates generally to shutter assemblies and more particularly to photographic-type shutter assemblies that rely on electromagnetic forces to open and close.
2. Description of Related Art
Electrically operated lens shutters used in various types of photographic and laboratory equipment are well known in the art. Lens shutters especially adapted for high speed opening and closing can operate in fractions of a second. An open/close cycle can take place in 30-40 milliseconds or less and repeated cycles at frequencies of 30 cycles per second are common.
Lens shutters generally are of two types. In one type, a so-called “guillotine” shutter has one or two thin, metal blades or leaves arranged to cover a lens opening. Pivot connections allow each blade to swing between a closed position where the blades cover the lens opening and an open position where the blades are drawn aside from the lens opening.
In a second type of shutter, a plurality of pivotally mounted blades are arranged around the lens opening. Each blade is connected to a rotatable drive ring. In the operation of these shutters, the rotation of the drive ring in one direction causes the blades to swing in unison to an open position. Counter rotation of the ring swings the blades to a closed position over the lens opening after exposure. Generally a linear electric motor is used to activate the shutter. When activated, the linear motor pulls on a lever arm that rotates the drive ring to open the shutter. To close the shutter the motor is deactivated and a spring causes the counter rotation of the drive ring to close the shutter. As noted above, shutters of this sort can cycle open and close 30 times per second.
In some applications, however, space is limited. Space limitations, particularly in the region of the shutter opening, dictate the parameters of size and placement of components for opening and closing the shutter. For example, components placed near the shutter opening must have a relatively low profile so as not to interfere with the cone angle of the light passing through the open shutter. Space limitations also complicate the substitution of one shutter assembly for another as in changing shutter size while maintaining the same base structure.
As noted above, existing shutter assemblies typically mechanically couple a linear electric motor to the shutter for opening and closing the lens opening. However, for proper operation, particularly at high speeds, the mechanical linkage must be precisely made and the movement of the linkage must be dampened by relatively large dampening assemblies.
Alternatively, other known shutter assemblies may utilize electro-magnetic energy to open and close the shutter. For example, such assemblies may include a permanent magnet disposed on a drive ring and a pair of spaced solenoids disposed above the permanent magnet. A polarity of an operative end of the first solenoid can be opposite that of an operative end of the second solenoid, such that the permanent magnet is attracted to one of the solenoids and repelled by the other. The solenoids can be energized to switch polarities, to effectuate a movement of the permanent magnet between a first position proximate the first solenoid and a second position proximate the second solenoid.
Such assemblies may be configured to open and close shutters at relatively high speeds without damaging the shutter blades. However, such assemblies generally require that the solenoid be situated in a tier or layer of the shutter assembly separate from, and either above or below, the permanent magnet. This necessarily increases the overall thickness of the shutter assembly.
Accordingly, the disclosed system and method are directed towards overcoming one or more of the problems set forth above.